Recent years have witnessed an explosive growth of mobile computing and the emergence of new wireless technologies. The desire to be connected any time, any where and in any way, leads to an increasing array of heterogeneous systems, application, devices and operators. Such heterogeneity is not likely to disappear in the foreseeable future because the variety of application requirements makes it difficult to find an optimal and universal solution. Likewise, an eagerness to capture the market encourages competing organizations to release non-interoperable systems. As a result, the ability to provide seamless telecommunication services in such a heterogeneous environment may be important to the success of the next generation of mobile communication systems.
Mobile IP is a current standard for supporting mobility in IP networks. Mobile IP defines a home agent and a foreign agent. The packets destined for a mobile host are intercepted by the home agent and tunneled to the foreign agent. The foreign agent de-capsulates the packets and forwards them directly to the mobile host. Mobile IP may provide a framework for allowing users to roam outside the home networks without disruption to their applications. However, known Mobile IP protocol networks are built with the wired Internet in mind where the end host's mobility is limited and infrequent. Furthermore, the Mobile IP protocol does not utilize network topology information and produces global updates whenever local mobility occurs, e.g., mobility between adjacent base stations in the same administration domain. Likewise, Mobile IP has no support for quality of service (QOS) features, such as high bandwidth requirements, high reliability requirements, and the like.
Mobile IP does not support QOS because it treats different forms of mobility uniformly, and produces a new care-of-address for every handover from one base station to another. Therefore, a user moving a short distance, e.g., between two adjacent base stations in the same administration domain, can experience significant disruption, e.g., loss and/or delay of signal, due to the frequent registration to the remote home agent. Likewise, creating a new care-of-addresses for every handover introduces complexity and delay for a new QOS reservation or path setup.
Known solutions include Cellular IP, Hawaii and other micro-mobility related protocols. Such protocols attempt to limit the global updates because of local movement by either introducing hierarchical foreign agents or smart foreign agents depending on the network topology. But the known schemes are based on homogeneous networks and the same administration domains. In other words, the known schemes attempt to solve the horizontal handover problems but do not address vertical handover, e.g., handovers between base stations under different administration domains. When vertical handover occurs, known schemes no longer work because no common agent exists above two separate administration domains. When vertical handover occurs, the mobile agent needs to rely on the Mobile IP to resolve macro-mobility issues. To enable seamless service, QOS capabilities should be provided during vertical handover.
RSVP is the current standard for supporting Inte-Serv in an IP network. It is known that to provide guaranteed service, reservation or admission control is needed at the edge router regardless of the QOS mechanism used in the core network. RSVP or its extension is a popular signaling protocol used by a host to request specific QOS capabilities from the network for particular application data streams. RSVP is also used by routers to deliver QOS requests to all nodes along the path of the data streams and to establish and maintain a state to provide the requested services.
A second set of protocols includes MRSVP, RSVP-A and other modifications to the RSVP signaling protocol. Because the RSVP protocol is designed without the consideration of mobility by its receiver-initiating algorithm, MRSVP and its relatives are proposed to support mobility. These protocols are based on proactively set up reservations, however, in base stations where the application is likely to travel. Such proactive reservation could lead to bandwidth waste due to the large amounts of control messages needed to refresh the RSVP soft states.
Micro-mobility protocols only deal with mobility issues and have no intrinsic QOS support. This problem can be addressed to some extent by using a common agent and reusing the common network path before and after handover. The previous reserved path could be reused and QOS reservation and update information could be limited to local network. But the lack of QOS support during the handover period still exists. When the terminal moves from one base station to other base stations, packets in the previous base station are either dropped or forwarded to the new base station without QOS support. Micro-mobility protocols attempt to decrease packet loss but other QOS parameters such as bandwidth and delay are not considered. Likewise, no differentiation exists between the treatments of different applications. Different applications have different QOS parameters in terms of bandwidth, delay and loss so they are divided into QOS classes and receive differentiated service based on their classes. But known handover schemes treat applications the same which violates the philosophy of differentiation and may lead to unnecessary system overuse.
As discussed above, when vertical handover occurs, micro-mobility and its related QOS improving extensions could not be used because of the lack of common agent and common network path. Schemes such as RSVP, MRSVP and RSVP-A which produce global updates and introduce longer handover periods can be used. A problem occurs regarding how to provide QOS support during this handover period.
Moreover, the upper-layer adaptation ability could also be taken into account when adopting network layer QOS support. Since adaptation ability is a basic requirement for elements working in the mobile domain, the application, middleware, and transport layer are equipped with some degree of adaptation mechanisms to deal with the packet loss or delay. Without the consideration of the upper-layer's adaptation ability, IP layer handover adaptation may unnecessarily duplicate the mechanism or even deteriorate the upper-layer's performance.
To enable seamless communications, there is a need for a QOS support system to support vertical handovers caused by mobile terminals.